Silicon nitride is an important material for fabrication of masking layers and dielectric coatings for microelectronic devices and the production of high temperature refractories. The fabrication of masking layers and dielectric coatings is commonly accomplished by film deposition, usually from a mixture of silane and ammonia which is decomposed at high temperature. Many operation difficulties are encountered in producing silicon nitride by this method. For example, variables in the rates of reactivity at different temperatures, controlling flow rates of gas mixtures and the pyrophoric nature of silane all contribute to difficulties in preparing silicon nitride films of uniform quality.
One solution proposed to solve these problems was the use of trisilylamine as a source for silicon nitride, as disclosed in U.S. Pat. No. 4,200,666. This volatile precursor for silicon nitride was anticipated to be of utility in preparing films for microelectronics. However, trisilylamine is difficult to prepare and is pyrophoric.
The production of high temperature refractories from silicon nitride suffers from some of the same difficulties. A proposed method which is more appropriate for silicon nitride refractories is disclosed in U.S. Pat. No. 3,892,583, and in a different variation described by Seyferth et al., "A Liquid Silazane Precursor to Silicon Nitride," Communications of the American Ceramic Society, page C-13 (January 1983). In these methods a resinous polysilazane of unknown structure is prepared in relatively low yield and then pyrolyzed to form silicon nitride. However, resins of this type, particularly those described by Seyferth et al., suffer from stability problems.
Another potential source for silicon nitride is through the decomposition of cyclic and polymeric diorganosilazanes. These compounds are considered by Zhinkin et al. Plasticheski Massy 12:16-17 (1963) and include the class of compounds represented by the following general formula: ##STR2## wherein R is an organic moiety, particularly alkyl, and n=3-4.